Seal Assembly for a Fluid Pressure Control Device

ABSTRACT

A seal assembly for a fluid pressure control device includes a guide element having a scaling surface and a first guide surface. A throttling element assembly includes a throttling element positionable within a fluid flow path, the assembly defines a mating surface adapted to seal with the sealing surface, and a second guide surface sized to slidingly engage the first guide surface. A relief void is formed in at least one of the guide element and the throttling element assembly adjacent the first and second guide surfaces to receive loose solid material, to thereby prevent disruption of the seal formed between the sealing surface and the mating surface.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a divisional application of co-pending U.S.patent application Ser. No. 10/985,305, filed Nov. 10, 2004, the entirecontents of which are hereby incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to fluid pressure controldevices and, more particularly, to assemblies for sealing betweensliding components used in such devices,

BACKGROUND OF THE DISCLOSURE

Fluid pressure control devices, such as control valves at-d regulators,are commonly used to control the flow characteristics of a fluid. Atypical device includes a valve body defining an inlet, an outlet, and afluid flow path extending between the inlet and the outlet. A valve seatis coupled to the valve body and defines an orifice through which theflow path travels. A throttling element, such as a plug, is moveablerelative to the valve seat thereby to control fluid flow through theorifice. In a sliding-stem fluid control device, the throttling elementis coupled to a stem extending outside the valve body, which in turn iscoupled to an actuator for positioning the throttling element relativeto the valve seat.

Sliding stem fluid control devices often require components for guidingthe throttling element assembly with respect to the valve seat. Inparticular, it is desirable to guide the linear movement of thethrottling element assembly so that it is concentric with the bonnet,packing bore, cage, seat ring, or other component coupled to the valvebody. Close guiding of the stem and/or plug tip also maintains maximumlateral stability to resist vibration and fatigue failures, Accordingly,components which guide movement of the throttling element often includeguide surfaces that slide against one another.

Rubbing and sliding of guide components in fluid control devices maycause material from the valve components to become free due to wear,galling, or other causes. The non-corrosive materials used for someapplications are particularly susceptible to galling. Galling and otherwear phenomena can cause movement and transfer of component materialalong the contact path. The loose material may degrade or disrupt sealedengagements within the fluid control device, such as the primary sealbetween a throttling element and seat, a secondary seal between athrottling element and cage, or a stem packing seal between a stem andpacking assembly, to name a few.

Conventional approaches to reduce galling typically employ the use ofdissimilar materials for the components which contact one another. Thispractice can result in higher cost materials and assembly, and may limituse of the device in certain applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view, in cross-section, of a fluid controldevice having a relief void positioned adjacent the contact surfacebetween a plug and seat;

FIG. 2 is an enlarged view of a detail of FIG. 1 illustrating the reliefvoid;

FIG. 3 is a side elevation view, in cross-section, of a secondembodiment of a fluid control device having a relief void positionedbetween a plug and cage;

FIG. 4 is an enlarged view of a detail of FIG. 3 illustrating the reliefvoid; and

FIG. 5 is a side elevation view, in cross-section, of a furtherembodiment of a fluid control device having a relief void positionedadjacent the stem and packing assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A seal assembly for a fluid control device is disclosed which includes arelief void for reducing the deleterious affects of galling or otherwear damage to sealed contact areas within the device. The relief voidprovides a space into which material, typically metal material, fromcomponents in contact may collect, thereby preventing the material fromentering areas intended for sealed contact. For example, the relief voidmay be positioned adjacent the sealed contact area between a plug andvalve seat, between a plug and cage, or between a stem and packingassembly. While these exemplary embodiments are described in greaterdetail below, it will be appreciated that the relief void may be locatedin other areas within a fluid control device that would benefit from thebenefits taught herein.

FIGS. 1 and 2 illustrate a sliding-stem, single port, unbalanced plugcontrol valve 10 having a valve body 12 defining an inlet 14 and anoutlet 16, wherein the valve 10 controls fluid flow from the inlet 14 tothe outlet 16. A valve seat 18 is coupled to the valve body 12 anddefines an orifice 20 through which the flow path passes. In theillustrated embodiment, the valve seat 18 is coupled to the valve body12 by a threaded engagement, however other known coupling methods may beused. An upper portion of the valve seat 18 is formed with a sealingsurface 22, which has a frostoconical shape in the exemplary embodiment.A lower portion of the valve seat 18 is formed with a cylindricalinterior surface 24.

A throttling element assembly 26 is inserted through a top port 28 ofthe valve body to control fluid flow through the valve seat orifice 20.The throttling element assembly 26 includes a throttling element, suchas plug 30, coupled to a stern 32. The plug 30 includes a mating surface34 that is shaped to complement the valve seat sealing surface 22, SOthat the mating surface 34 sealingly engages the sealing surface 22 toform a primary seal when the plug 30 is in the closed position, asillustrated in the FIG. 2. The plug 32 also includes a cylindricalexterior surface 36 sized to slidingly engage the valve seat interiorsurface 24. In this embodiment, the interior surface 24 of the valveseat 18 and the exterior surface 36 of the plug 30 provide first andsecond guide surfaces which direct the plug mating surface 34 toward thevalve seat sealing sur:face 22 as the throttling element assembly 26moves to the closed position.

In the embodiment illustrated in FIG. 1, the plug 30 further includesflow characterizing legs 38 extending downwardly from the exteriorsurface 36. The legs 38 are shaped to form gaps 40 therebetween, therebyto obtain desired flow characteristics when the throttling elementassembly 26 is only partially open, as is well known in the art. It willbe appreciated that other types of plugs, with and without flowcharacterizing legs, may be used without departing from the scope of thepresent disclosure.

The stem 32 extends from a top surface of the plug 30 and through thevalve body top port 28. A free end 42 of the stem 32 is adapted forcoupling to an actuator (not shown) which provides a motive force to thethrottling element assembly 26.

A bonnet assembly 43 is coupled to the valve body 12 to enclose the topport 28 and to seal with the stem 32. The bonnet assembly 42 includes abonnet 44 releasibly coupled to the body 12, such as by fasteners. Thebonnet 44 has an inner bore 48 defining a packing chamber 50 and a neck52. The neck 52 may slidingly engage the stem 32 to provide additionalguidance to the throttling element assembly 26 during movement, asdiscussed in greater detail below with reference to the embodiment ofFIG. 5. A packing assembly 54 may be inserted into the packing chamber50 to seal between the valve stem 32 and the bonnet inner bore 48 toprevent leakage of fluid therethrough.

A relief void 56 is formed in the valve seat 18 to reduce the risk offreed material, such as from galling, from entering the primary sealarea. As illustrated in FIGS. 1 and 2, the relief void 56 is formed as agenerally annular groove which creates a gap between the plug exteriorsurface 36 and the valve seat interior surface 24. The void 56 has avolume sufficient to receive material from the plug 30, the valve seat18, or other component that may be loosened or otherwise transferredduring operation of the throttling element assembly 26.

In the exemplary embodiment the relief void 56 is positioned between theprimary seal formed by the sealing surface 22 and mating surface 34 andthe guide surfaces provided by the plug exterior surface 36 and thevalve seat interior surface 24. Accordingly, material freed by galling,wear, or other causes, which will typically originate in the area of theguide surfaces, will collect in the relief void 56, thereby avoidingdisruption of the primary seal. Material deposited in the relief void 56may be subsequently removed by process fluid flow or may remain in therelief void indefinitely. While the exemplary embodiment shows therelief void 56 positioned immediately adjacent the primary seal, it willbe appreciated that the relief void 56 may have other locations, as longas it is proximate either the guide surfaces or the sealing surfaces.Furthermore, while the relief void 56 is shown as formed in the valveseat 18, it may additionally or alternatively be provided in the plug30. Accordingly, the same or similar materials may be used for the valveseat 18 and plug 30, such as 316 Stainless Steel, 304L Stainless Steel,Stainless Steel Alloy 20, or the like.

FIGS. 3 and 4 illustrate an alternative embodiment of the seal assemblyincorporated into a valve 110 having a cage-style trim and balancedvalve plug. The valve 110 includes a valve body 112 defining an inlet114 and an outlet 116, wherein the valve controls fluid flow from theinlet 114 to the outlet 116. A valve seat 118 is coupled to the body 112and defines an orifice 120 through which the flow path passes. Again,while the valve seat 118 is illustrated as being coupled to the valvebody 112 by a threaded engagement, other known types of couplings may beused. The valve seat 118 includes a sealing surface 122.

A throttling element assembly 126 and a cage 160 are inserted through atop port 128 of the valve body 112 to control fluid flow through thevalve seat orifice 120. The cage 160 includes a flange 162 that iscoupled to and substantially closes off the body top port 128. Acylindrical wall 164 extends downwardly from the flange 162 and has abottom edge 166 that is spaced from the valve seat 118 when assembled,thereby to allow fluid flow therebetween. The cylindrical wall 164further defines an interior surface 168. The cage 160 also includes aboss 170 having a center bore 172 formed therein. The center bore 172 issubstantially concentric with the interior surface 168 and defines apacking chamber 150 and a neck 152.

The throttling element assembly 126 includes a throttling elementmoveable within the fluid flow path. The throttling element, such as aplug 130, is coupled to a stem 132 which extends from a top surface ofthe plug 130 and through the valve body top portion 128. A free end 142of the stem 132 is adapted for coupling to an actuator (not shown) whichprovides a motive force to the throttling element assembly 126. A bottomportion of the plug 130 includes a mating surface 134 that is shaped tocomplement the valve seat sealing surface 122, so that the matingsurface 134 sealingly engages the sealing surface 122 to form a primaryseal when the plug 130 is in the closed position. The plug 132 alsoincludes a balance port 133 which allows fluid to flow into an upperchamber 135 defined by the cage 160 and an upper surface of the plug130.

The plug 130 includes a guide ring 137 defining an exterior surface 136sized to slidingly engage the cage interior surface 168. In thisembodiment, both the guide ring 137 and the cage interior surface 168are cylindrical to provide first and second guide surfaces adapted todirect the plug mating surface 134 toward the valve seat sealing surface122 as the throttling element assembly 126 moves the closed position.

The plug 130 also includes a seal ring 139 for preventing fluid leakagethrough a secondary flow path between the cage 160 and plug 130. Theseal ring 139 is also generally cylindrical and defines a second matingsurface 141 sized to slidingly engage and seal with the cage interiorsurface 168. The seal ring 139 may be formed of a material thatadequately seals with the metal cage material while allowing slidingalong the cage interior surface 168. Possible materials include afluoropolymer resin, such as the TEFLON® product marketed by DuPont, agraphite material or nitrile rubber.

A first relief void 156 is formed in the plug 130 to reduce the riskfree material from entering the secondary seal area of contact betweenthe seal ring 139 and the cage interior surface 168. As best illustratedin FIG. 4, the relief void 156 is formed by an intermediate recessedportion 158 of the plug 130. The intermediate recessed portion 158creates a generally annular groove having a volume sufficient to receivematerial from either the plug 130, the cage 160, or other valvecomponents that may be loosened or otherwise transferred duringoperation of the throttling element assembly 126. In the illustratedembodiment, the first relief void 156 is positioned between the guidering and the seal ring, however the alternative locations noted abovewith respect to the embodiment of FIGS. 1 and 2 may also be used.

To further protect the sealed contact between the seal ring 139 and thecage interior surface 168, a second relief void 190 may also beprovided. As illustrated in FIGS, 3 and 4, the second relief void 190 isformed by a top portion 192 of the plug 130 having a reduced diameter.As with the first relief void 156, the second relief void 190 creates agap between the plug 130 and the cage interior surface I 16 which mayreceive material Freed by galling, wear, or other causes.

An additional embodiment of a seal assembly for use in a fluid controldevice is illustrated in FIG. 5, which shows an enlarged elevation view,in cross-section, of a sealed contact between a packing assembly 210 anda stem 211, The stem 211 is part of a throttling element assemblyincluding a throttling element (not shown). A bonnet 212, which may becoupled to a valve body (not shown), includes a center bore 214 sized toreceive the valve stem 211. The center bore 214 defines a packingchamber 218, a neck 220, and a receptacle 222. The packing assembly 210maybe inserted into the packing chamber 218 to seal between the valvestem 211 and the inner bore 214, thereby to prevent leakage of fluidtherebetween.

The illustrated packing assembly 210 includes a V-ring 230, a maleadaptor 232, a female adaptor 234, upper and lower anti-extrusion rings236, and a packing box ring 238, however, other known packing boxcomponents may be used without departing from the present disclosure. Inoperation, the packing assembly 210 is compressed so that an interiormating surface 240 of the V ring 230 sealingly engages an exteriorsealing surface 242 of the stem 211. Material for the V ring 230 isselected so that it provides a good seal with the stem while allowingthe stem to slide.

A bearing ring 246 is inserted into the receptacle 222 for furtherguiding the stem 211 during travel. As such, the bearing ring 246includes an interior surface 248 that closely fits an exterior surfaceof the stem 211, yet allows the stem to slide. Accordingly, the interiorsurface 248 and stem exterior surface provide guide surfaces fordirecting sliding movement of the throttling element assembly,

A relief void 250 is formed adjacent the interior surface 248 forreceiving loosened material, thereby reducing the risk of degrading thepacking assembly/stem seal. The relief void 250 is formed as an enlargeddiameter portion of the interior surface 248, which creates an annulargroove. The groove defines a gap between the bearing ring interiorsurface 248 and the stem exterior surface having a volume sufficient toreceive valve material loosened during operation. In this embodiment,the relief void 250 is positioned immediately adjacent the guidingsurfaces defined by the bearing ring interior surface 248 and the stemexterior surface, which are slightly spaced from the sealed contactbetween the packing assembly and stem.

The foregoing detailed description has been given for clearness andunderstanding only, and no unnecessary limitations should be understoodtherefrom, as modifications would be obvious to those skilled in theart.

1. A fluid pressure control device comprising: a body defining an inlet,an outlet, and a fluid flow path extending from the inlet to the outlet;a guide element coupled to the body and comprising a cage having aninterior surface defining a sealing surface and a first guide surface;and a plug assembly comprising a plug positionable within the flow pathand coupled to a stem, the plug assembly defining a mating surface and asecond guide surface, the mating surface adapted to seal with thesealing surface of the guide element, the second guide surface sized toslidingly engage the first guide surface of the guide element; wherein arelief void is formed in at least one of the guide element and the plugassembly adjacent the first and second guide surfaces.
 2. The fluidpressure control device of claim 1, wherein the plug assembly comprisesa guide ring and a seal ring, the guide ring sized to slidingly engagethe cage interior surface, thereby defining the second guide surface,and the seal ring having an exterior surface sized to slidingly engageand seal with the cage interior surface, thereby defining the matingsurface.
 3. The fluid pressure control device of claim 2, wherein therelief void is defined by a first recessed portion formed in the plug.4. The fluid pressure control device of claim 3, wherein the firstrecessed portion of the plug is positioned adjacent the seal ring. 5.The fluid pressure control device of claim 3, wherein the first recessedportion of the plug is positioned between the guide ring and the sealring.
 6. The fluid pressure control device of claim 4, furthercomprising a second relief void defined by a second recessed portionformed in the plug, the second recessed portion of the plug formedopposite the seal ring from the first recessed portion of the plug.
 7. Afluid pressure control device comprising: a body defining an inlet, anoutlet, and a fluid flow path extending from the inlet to the outlet; aguide element coupled to the body and comprising a packing assemblydefining a sealing surface and a first guide surface; and a plugassembly comprising a plug positionable within the flow path and coupledto a stem, the stem having an exterior surface defining a mating surfaceid a second guide surface, the mating surface adapted to seal with thesealing surface of the packing assembly, the second guide surface sizedto slidingly engage the first guide surface of the packing assembly;wherein a relief void is formed in at least one of the guide element andthe plug assembly adjacent the first and second guide surfaces.
 8. Thefluid pressure control device of claim 7, wherein the sealing surfaceand the first guide surface are defined by a same interior surface ofthe packing assembly and, wherein the mating surface and the secondguide surface are defined by a same portion of the stem exteriorsurface.
 9. A seal assembly for a fluid pressure control device having abody defining an inlet, an outlet, and a fluid flow path extending fromthe inlet to the outlet, the seal assembly comprising: a guide elementcoupled to the body and comprising a cage having an interior surfacedefining a sealing surface and a first guide surface; and a throttlingelement assembly including a plug assembly positionable within the flowpath, the plug assembly defining a mating surface and a second guidesurface, the mating surface adapted to seal with the guide elementsealing surface, the second guide surface sized to slidingly engage thefirst guide surface of the guide element; wherein a relief void isformed in at least one of the guide element and the throttling elementassembly adjacent the first and second guide surfaces.
 10. The sealassembly of claim 9, wherein the plug assembly further comprises a plug,a guide ring, and a seal ring, the guide ring sized to slidingly engagethe cage interior surface, thereby defining the second guide surface,and the seal ring having an exterior surface sized to slidingly engageand seal with the cage interior surface, thereby defining the matingsurface.
 11. The seal assembly of claim 10, wherein a first recessedportion of the plug forms the relief void.
 12. The seal assembly ofclaim 11 wherein the first recessed portion of the plug is positionedadjacent the seal ring.
 13. The seal assembly of claim 11, wherein thefirst recessed portion of the plug is positioned between the guide ringand the seal ring.
 14. The seal assembly of claim 12, further comprisinga second relief void formed by a second recessed portion of the plug,the second recessed portion of the plug formed opposite the seal ringfrom the first recessed portion of the plug.
 15. A seal assembly for afluid pressure control device having a body defining an inlet, anoutlet, and a fluid flow path extending from the inlet to the outlet,the seal assembly comprising: a guide element coupled to the body andcomprising a packing assembly defining a sealing surface and a firstguide surface; and a throttling element assembly comprising a throttlingelement positionable within the flow path and a stem coupled to thethrottling element, the stem having an exterior surface defining amating surface and a second guide surface, the mating surface adapted toseal with the sealing surface of the guide element, the second guidesurface sized to slidingly engage the first guide surface of the guideelement; wherein a relief void is formed in at least one of the guideelement and the throttling element assembly adjacent the first andsecond guide surfaces.
 16. The seal assembly of claim 15, wherein thesealing surface and the first guide surface are defined by a sameinterior surface of the packing assembly, and wherein the mating surfaceand the second guide surface are defined by a same portion of the stemexterior surface.